Several publications and patent documents are referenced in this application in order to more fully describe the state of the art to which this invention pertains. The disclosure of each of these publications and documents is incorporated by reference herein.
Mycobacterium tuberculosis (Mtb) is one of the world's deadliest pathogens, claiming about 1.5 million lives annually (Dye et al., Lancet Infect Dis 8, 233 (April, 2008). The occurrence of approximately 9 million new cases of Mtb a year and the increased emergence of antibiotic resistant strains necessitates the development of new anti-mycobacterial drugs. The Mtb proteasome and proposed cofactors, Mycobacterium proteasomal ATPase (Mpa) and proteasome accessory factor A (PafA), are essential for the pathogenicity of Mtb (Darwin et al., Science 302, 1963 (2003); Darwin et al, Mol Microbiol 55, 561 (2005); Gandotra et al, Nat Med 13, 1515 (December, 2007)), qualifying components of the Mtb proteasome system as potential drug targets.
Similar to the eukaryotic 20S proteasome, the Mtb proteasome is a multi-subunit barrel-shaped protease composed of two rings of catalytic β-subunits sandwiched by rings of α-subunits (Benaroudj et al, Mol Cell 11, 69 (January, 2003); Groll et al., Nature 386, 463 (Apr. 3, 1997); Hu et al., Mol. Microbiol. 59, 1417 (2006); Lin et al., Mol. Microbiol. 59, 1405 (2006); Unno et al., Structure 10, 609 (May, 2002)). The eukaryotic 26S proteasome is composed of a 20S core particle and one or two 19S regulatory caps, which include ATPases that recognize, unfold, and translocate substrates into the core for degradation [reviewed in Baumeister et al., Cell 92, 367 (1998)]. In Mtb, Mpa shares homology with regulatory cap ATPases that translocate proteins into the core. The present inventors previously identified substrates of the Mtb proteasome (Pearce et al., EMBO J. 25, 5423 (2006)), however, the mechanism(s) whereby these substrates were targeted for degradation was not elucidated. Proteins delivered to the eukaryotic proteasome are usually conjugated with ubiquitin, which covalently attaches to substrate lysines (Lys) as well as onto ubiquitin itself [reviewed in Hershko et al, Annu Rev Biochem 67, 425 (1998)]. Ubiquitin-like genes have not been identified in the Mtb genome, suggesting that substrate targeting to the Mtb proteasome occurs via an ubiquitin-independent mechanism.
The special properties of the Mtb cell wall combined with its extremely slow dividing time make efficient treatment of tuberculosis (TB) difficult. Current therapies make use of a combination of antibiotics that have to be taken daily for multiple months. The treatment has significant toxicity and is often accompanied with severe side effects. Moreover, multidrug-resistant strains of Mtb have developed. Therefore, the need for new TB drugs that inhibit targets that are different from those of currently used drugs is urgent. To minimize side effects, these new targets should ideally only be present in the disease causing bacteria and not in the human host.